X-ray microfluorescence is a non-destructive technique known in the art for determining the atomic composition and thickness of thin films. Typically, a focused x-ray beam is directed at a sample, and the x-ray fluorescence induced by the interaction of the x-rays with the sample is detected by a detector located near the sample. The composition and thickness of the irradiated sample are determined from the intensity and energy of the fluorescent x-ray photons.
In "Annular-type solid state detector for a scanning x-ray analytical microscope," Rev. Sci. Instrum. 66(9) (September, 1995), pp. 4544-4546, which is incorporated herein by reference, Shimomura and Nakazawa describe an annular germanium detector located near an irradiated sample which transduces the energy resulting from x-ray fluorescence into a single channel of data.
In the article, "X-ray microfluorescence analyzer for multilayer metal films," Thin Solid Films 166 (1988), pp. 263-272, which is incorporated herein by reference, Cross and Wherry describe a system wherein a lithiumdoped silicon crystal detector captures photons emitted from a sample exposed to x-rays.
U.S. Pat. No. 5,497,008, to Kumakhov, which is incorporated herein by reference, describes analytic instruments using a polycapillary x-ray optic, also known as a Kumakhov lens, for x-ray fluorescence analysis or spectroscopy. The instruments described use a single fluorescence detector.
A single x-ray photon produces many electron-hole pairs in a semiconducting detector, and analysis of the associated current pulse shape enables the detector to measure the x-ray photon energy. However, semiconducting x-ray detectors, such as the detectors described above, are subject to "pile-up" of data, which occurs when the x-ray photons are temporally too close together for satisfactory discrimination of the current pulses created.